This application is based on application No. 131475 filed in Japan on Apr. 28, 2000, the content of which incorporated hereinto by reference.
This invention relates to a battery pack having a case which holds a plurality of circular cylindrical batteries and a printed circuit board.
A battery pack having a case which holds a plurality of circular cylindrical batteries is used for a variety of applications. For each application, it is important to make battery pack charge-discharge capacity large and external size small. In addition, external shape and battery capacity are determined by the electrical equipment the battery pack is attached to. This allows the battery pack to attach to a specific location on the electrical equipment. In prior art battery packs, batteries are lined up parallel to each other and held in a case with no space between batteries. Cylindrical batteries held in a battery pack case and arranged in this manner and are not always in an ideal environment for charging and discharging in all applications. This is because heat evolved from interior batteries is not effectively carried away. Batteries located at the periphery effectively transfer heat to the outside of the case. However, a battery disposed at the interior is surrounded by other batteries which have risen in temperature, and the interior battery itself also emits heat. Consequently, heat cannot be effectively transferred away from an interior battery and its performance can easily degrade due to high temperature effects. This drawback can be eliminated by providing gaps between batteries. However, if gaps are provided between batteries, the battery pack grows unduly in size.
The present invention was developed to resolve these types of drawbacks. Thus it is a primary object of the present invention to provide a battery pack which holds batteries inside a case in an ideal arrangement, and which allows effective heat transfer away from batteries disposed at the interior while minimizing size increase in the battery pack outline.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The battery pack of the present invention holds batteries in a case with a first block, which is a plurality of circular cylindrical batteries arranged in the same horizontal plane, and a second block, which is an equivalent configuration of a plurality of circular cylindrical batteries arranged in the same horizontal plane, disposed in an adjacent fashion and in the same horizontal plane. The first and second blocks are provided with N+M circular cylindrical batteries. N+M circular cylindrical batteries are arranged with N batteries lined up side-by-side in parallel fashion to form a lateral battery array, and M perpendicular batteries in close proximity to an electrode end of the lateral battery array and orthogonal to that lateral battery array. The batteries of the first block and the second block are disposed in a rectangular case with point-by-point symmetry about the center-point of the case. Further, an electrode end of the perpendicular batteries protrudes from a side of the lateral battery array towards the side of the adjacent block to create space at the center region between the first and second blocks.
In this patent application, the lateral direction is taken to be the direction of the diameter of a circular cylindrical battery, and the lengthwise direction is taken to be the longer direction of the cylinder axis. Consequently, a lateral battery array means a plurality of batteries lined up side-by-side (not end-to-end) in parallel fashion.
This configuration of battery pack is characterized by holding circular cylindrical batteries in an ideal arrangement, by making the battery pack outline as compact as possible, and by allowing effective heat removal from batteries disposed at the center region. This is because the plurality of circular cylindrical batteries of the battery pack of the present invention are divided into a first block and a second block, and the batteries of the first and second blocks are configured as lateral battery arrays and perpendicular batteries. The batteries of the first and second block are arranged with point-by-point symmetry about the center-point of a rectangular case. In addition, space is provided at the center region between the first and second blocks by protrusion of electrode ends of perpendicular batteries from the sides of lateral battery arrays towards the side of the adjacent block. The center space provided at the center region of the case prevents batteries in that center region from being heated by adjacent batteries, and effectively prevents interior battery degradation due to heating. Consequently, the battery pack of the present invention has the characteristic that high current charging and discharging can be performed without battery performance degradation.
Preferably, circular cylindrical batteries with a length dimension greater than three times the diameter but less than four times the diameter are used for the battery pack of the present invention. In this battery pack, preferably N is 3 and M is 1. Specifically, 3 batteries are lined up side-by-side in a parallel fashion as the lateral battery array, and 1 perpendicular battery is disposed at a right angle to this lateral battery array.
It is also preferable to structure the case of the battery pack of the present invention with a first case and a second case. A wall is provided in the center region space and is formed as a single piece with the first case. Connecting hooks which mate with the wall are formed as a single piece with the second case. The first case and the second case of this battery pack can be reliably connected by joining the connecting hooks to the wall.
Since the first and second cases can be connected at the wall provided in the center region space of this configuration of battery pack, it has the characteristic that the case can be made thin while effectively preventing case deformation such as case expansion.
Further, lead wires are preferably disposed in the center region space of the battery pack of the present invention. This configuration of battery pack is characterized by using the center region space for lead wire disposition and allowing simplified routing of those lead wires.